Measuring roughly fifteen metres east to west and four and a half metres north to south, and sinking no more than half a metre at its deepest, the depression is easy to overlook. Its gently sloping sides and broadly level base, with a slight rise off-centre to the west, are the kind of detail that rewards a careful eye rather than a casual glance. What it likely marks is the partial collapse of a souterrain, an underground passage or chamber constructed during the early medieval period, typically from dry-stone walling and roofed with large lintels. Souterrains were built for a variety of purposes, most probably for cool storage and as places of refuge, and they survive across Ireland in varying states of preservation.

The souterrain sits within a rath, the remains of an earthen ringfort that has been recorded separately. Raths were the enclosed farmsteads of early medieval Ireland, usually circular in form and defined by one or more banks and ditches. The presence of a souterrain within the interior of a rath is a common enough arrangement, but the relationship between the two features at Roxborough gives some sense of how the site was once organised as a functioning settlement. The depression lies just off-centre to the west of the rath, which is where a collapse into the underlying structure has most visibly expressed itself at the surface.